1. Field of the Invention
The present invention relates to a lens driver which converts rotation of a manually operated ring into pulse signals and drives a lens on the basis of the pulse signals.
2. Description of the Related Art
Conventionally, a lens driver which converts rotation of a manually operated ring into pulse signals and drives a lens on the basis of the pulse signals has been known (see, for example Japanese Unexamined Patent Application Publication No. Hei-4-281416 (hereinafter referred to as Patent Document 1)).
It is difficult to drive a motor according to the amount of rotation of the manually operated ring with high fidelity, stop the motor in a focused state, and maintain the focused state. In order to solve this problem, the lens driver disclosed in this Patent Document 1 is configured such that the driving of the motor is forcibly stopped once the focused state is detected.
In addition, as this type of lens driver, there are also known a lens driver which can provide two-step driving speed according to a rotation angle of a manually operated ring and a lens driver of two-phase pulse system which determines driving speed of a lens according to rotating speed of a manually operated ring (see, for example, paragraphs to [0009], [0011], [0065], and [0070] of Japanese Patent Application Publication No. 2001-166196 (hereinafter referred to as Patent Document 2)).
In the lens driver of the two-phase pulse system with the manually operated ring, two-phase pulses corresponding to the rotating speed of the manually operated ring are outputted from an encoder, rotation direction and rotating speed are detected on the basis of the pulse signals, and a lens is driven by a motor as lens driving means.
In the lens driver disclosed in Patent Document 2, the lens is switched to move, at high speed for the photographing on the telescopic side where lens driving amount is large, and at low speed or the photographing on the wide angle side where lens driving amount is small. In addition, the lens is switched to move at higher speed for the macro photographing involving a large amount of lens extension than for the non-macro photographing. In these ways, the lens driver disclosed in Patent Document 2 achieves swift lens driving with a manually operated ring for the macro photographing.
Thus, the conventional lens driver has the following problem in performing a focusing operation using a manually operated ring (also referred to as an MF ring) when employed in a camera with a high-power zooming function or a camera equipped with a macro photographing mode. To be specific, the conventional lens driver has difficulty in swift focusing during telephoto zooming and in macro photographing because a lens movement amount is large, requiring much time for the lens movement.
The lens driver of two-phase pulse system has the following problems. Although moving time is reduced with high rotating speed of a manually operated ring, an object of accurately positioning a lens at a target focused position through fine adjustment cannot be achieved if the lens is driven at high speed regardless of the rotating speed of the manually operated ring. On the other hand, swift driving of the lens demanded by a user cannot be achieved if the driving speed is changed only depending on the speed of the manually operated ring rotated by a user.
In addition, in the conventional camera, the extension amount of a focus lens and a distance to a subject are coarsely correlated on the long distance side. That is to say, lens position resolution is coarse. To the contrary, on the short distance side, the extension amount of the focus lens and the distance to the subject are finely correlated, and thus the lens position resolution is dense.
Therefore, when the focus lens is moved by rotating the manually operated ring, pulse responsiveness on the long distance side is sensitive. Thus, when the focus lens position is on the long distance side, it is difficult to stop the focus lens at a desired position by operating the manually operated ring.
That is to say, in the conventional lens driver of the two-phase pulse system, the advantage of operating the manually operated ring has not been well utilized and it cannot be necessarily said that user friendliness is sufficient.